Glass seal for spark plug electrode assembly



R. TWELLS El' AL sept. 17, 1957 GLASS SEAL FOR SPARK PLUG ELECTRODEASSEMBLY i Filed May 2l, 1952 0 A m M #QM/MM f f f IN VEN TO Rabeff-TWe//s Frank C. Arrance BY 141114,

United rates Patent 2,806,971 Patented Sept. 17, 1957 GLASS SEAL FORSPARK PLUG ELECTRDE ASSEMBLY This invention relates to glass seals forspark plugs, more particularly to glass seals for center electrodespositioned in the bore of a ceramic insulator adapted for fabrication ina mass production line.

Glass seals for center electrodes for spark plugs are known in the priorart and have been used in a mass production line, but have had thedisadvantage that after the glass is fused it is necessary to placepressure upon the glass by mechanical means in order to have the glassengage the electrode and the insulator intimately to form the seal. Thiscould only be done outside of the furnace which meant manualmanipulation of parts at relatively high temperatures in order to applypressure `to the glass whichf is not an easy step -in `a mass productionline. Furthermore, the high temperatures of the metal parts, whenexposed to the atmosphere during the pressing oper ation, caused anexcessive oxidation of these metal parts, which destroyed theirappearance and also their electrical efliciency by creating contactdiiculty, so that a cleaning operation was required. Open electricalcircuits too were not uncommon.

The present invention contemplates a glass seal for spark plugs which issuited for mechanization in a mass production line and which obviatesthe diiliculties mentioned hereinbefore with reference to the prior art.The invention contemplates a process which is continuous rather than anintermittent one, so that the metal parts need not be removed from thefurnace at high temperatures into the atmosphere to become stronglyoxidized but remain in the furnace in a controlled reducing atmosphereuntil sulficiently cooled to be brought into the atmosphere withoutoxidation.

The invention further contemplates the provision of a glass seal usingmetallic connector elements in touching relation, through which anelectric circuit is to be established, which assures good conductivitybetween the elements after being subjected to the heat of fusion for theglass without the use of techniques which cannot be readily applied inthe furnace such as welding ctc.

The invention further contemplates the provision of a method of formingglass seals wherein an electric circuit is made between contactingelements by the use of sintered metal powders, which are compacted inposition to obviate shrink-age before tiring.

The invention further contemplates the provision of a method of making aglass seal with metallic elements in touching relation wherein glass andmetal powders are compacted in layers to obviate shrinkage and toprovide a seal by heating alone without mechanical compression afterfusion of the glass.

It is, therefore, a principal object of this invention to provide aglass seal for use in spark plugs wherein the elements of the seal arein powder form compacted in position around metallic elements and thenheated by passing through a high temperature zone to complete the seal.

It is a further object of this invention to provide a meth-od of sealingan electrode in the bore of an insulator of a spark plug which iscontinuous and in which the sealing elements are subjected to highfusing temperatures in a protective atmosphere wherein no mechanicalpressure is `applied at high temperatures.

Other objects and advantages of this invention relating to thearrangement, operation `and function of the related elements of thestructure, to various details of construction, to combinations of partsand to economies of manu- 1 acture, will be apparent to those skilled inthe art upon consideration of the following description iand appendedclaims, reference being had to the accompanying drawings forming a partof this specication wherein like reference characters designatecorresponding parts in the several views.

Referring to the drawings:

Fig. 1 isa sectional elevation showing `a preparatory step in carryingout the invention;

Fig. 2 is a similar View showing another preparatory step;

Fig. 3 is a sectional elevation of a completed spark plus;

Fig. 4 is a view similar to Fig. 3 showing a modification;

Fig. 5 is a sectional elevational view of a modification;

lFig. 6 is the same as Fig. 5 after mechanical compression; and

Fig. 7 is a sectional elevational view of still another modification.

In carrying out the invention, a spark plug insulator 10 is provided,such as shown in Figs. 1 and 5 of the drawings, illustrating two types-ofrinsulators capable of being utilized although the invention iscapable of being applied to insulators of all types wherein a metallicmember is to be sealed hermetically in a bore. Spark plug insulators arepreferably made of a high percentage of alumina bonded together into ahomogeneous body by agents having lower melting points, such as fluxesand the like, as are well known in the art.

The insulator l0 is provided with a longitudinal bore 12 which isprovided with an internal shoulder 14 adjacent the lower yend of theinsulator to provide a seat for a headed tiring electrode 16 positionedin the lower portion of the bore and adapted to project from theinsulator as is well known in spark plug construction. This firingelectrode is generally made of nickel-manganese alloys for durabilityagainst high temperatures and to prevent excessive erosion due to thespark.

The head -of the electrode is knurled at its outer perimeter 16A to forma mechanical interlock with the glass fused thereabout as will bedescribed further hereinafter. The head is also provided with ya pigtail18 preferably welded to its upper surface to project longitudinallyupwardly therefrom as is clearly shown in Fig. l. The pigtail 18 is ahair-like wire fabricated from a special alloy of iron-nickel and cobaltcommercially sold under the trade name Kovar and fully described inPatent No. 1,942,260 although it can also be lfabricated from molybdenumor tungsten if desired. This alloy and these pure metals are suitablefor use with borosilicate glasses to form glass to metal seals, while,yat the same time, the glass wets the bore of the insulator to form aseal between the ceramic and the metal to allow electrical connection tobe made with the electrode 16 while sealing the bore 12 of the insulatorto prevent escape of hot gases therethroughwhen the lspark plug is usedin an engine with the firing tip of the electrode and insulatorextending into the combustion chamber where relatively high pressuresare encountered.

The pigtail 13 is rst welded to the electrode 16 and p the assembly isthen dropped into the bore of the insulator as shown in Fig. 1. Theinsulator is then positioned on an anvil 20 in concentric relation witha ram Z2 which appliedl to the-ram` may vary and an impact blow is bestto obtain the greatest` density in the compacted' glass, vso thatshrinkage upon fusion is reduced to aminimum, if not completely obviat-V A l,

The depth-of the glass Vpack l24 mustl allow the pigtail to extendaboveit, as shown in` Eig. 1, so that electrical connection can be madetherewith. trical connection with the pigtaill 18,a body of compactedmetal-powder 26ina relatively thinlayer is utilized positioned" in thebore 12. around the terminus of the pigtail projecting above` ther packof `powdered glass-which has just been positioned in the bore asdescribed hereinabove. The same ram 22-can be used for this purpose or asolid ram 22A, Fig. 2, may be used. The metal powderto beusedrmust bevcapable of: being sintered` at the. temperature which willy fuse theglass toA make the seal.as..wil1=be' further described hereinafter, and'ironfhas been found to sinter successfully under these conditions.'

The iron utilized 1s finely; powdered and is compacted inv positionabove the glass to obtain maximum density under the compactingconditions. .Y Y

It may be desirable under. certain conditions to give the iron powderspecialV forms, such `as a cup shape 26A,l

as isshown in- Fig. 4, which can be obtained by using a special ram 22Bhaving a boss 22C on its lower end v tocompact the iron powder into thedesired shape, whichf it willvretain after tiring by'sinteringpermanently. For most'purpfo'ses, a simple layer of'sintered iron issatisfactory as-shown in Figs. 2u and 3. l

`rThe insulator is now ready for firing, which will fuse the glass and,in fusing, will wet both the pigtail 1S and the bore 12 ofthe insulatorto form a hermetic seal for the bore, through-which electric current canowrthroughthe agency of the metallic'pigtail.

will not shrink substantially inasmuch as the compacting ofthe powderedglass before tiring, as already described,

has-reduced the volume of the interstices to a minimum, sothatsubstantial shrinkage of the glass body is obviated. Firing alsosinters the powdered iron .layer to rigidity with close contact to theprotruding end of the pigtail .layer and' thev electrode 16 even at lowvoltages such as The glass is iinelyf To obtain this elec-V 'Ihe glass,by fusing,4

establishing an electrical circuit between the sintered iron 110 AQ C.whichis convenient to usefor automatic test- Y ing purposes in a massproduction line, so that noopen. circuitsy will pass the automatic testand ultimately result kin adefective spark plug.

The firing occurs in a furnace provided with. a protective atmospherereducingin nature, so that no oxides.

will formv on the metallic parts. The ytemperature kof ring is selectedby considering the nature of the glass constituents their fusingtemperature and the sintering temperature of the powdered-metal used inthe upper layer. The insulators are placed in the furnace on a simplebelt conveyor and are slowly heated to the required temperature andthenlallowed to remain in the protective atmos.

phere of the furnace until their temperature has dropped suiicientlylto` bring safely into the normal atmosphere without-oxidation of themetal parts. The process isi-a continuous one and very adaptable to amass productionfm TheV seal formed between these three elements, the Ainsulator-bore, the glass element, and the pigtail is abso line.

lute with zero leakage under all temperatures under which theYsparkplug. is required to operate. The insulator is one of the aluminatype having an expansion coborosilicate glasses having an expansioncoefficient of 3.0 to 6.7)(10-6 a preferred borosilicate glass having acoecient of 3.2 106 having 80.5% S102, 12.9% B203, 3.8% Na203, 0.4% KOand 2.2% A1203 sold as No. 7740 by Corning Glass works, Corning, NewYork. The pigtail of Kovar has an expansion coeicient of approximately3.5)(10-6. The coeicients of expansion are chosen to form a pressuretype seal, whereinthe insulator, being the largest and strongest elementof the combination, compresses the glassl and the glass compresses thepigtail, or the metallic member through a substantial portion ofthe'temperature range to which the sealis subjected when used in a sparkplug. Y

The layer of powdered glass and the layer of powdered metal can bepoured loosely into the bore of the insulator around the pigtail andthen compressed in one step rather than in several steps asdescribedfghereinbefore with the firing occurring thereafter. This is,however, notA as f efficient because` thedensity of th'e compactedVmaterial is not as great with the interstices between the particlesVbeinglarger 'resulting in morej shrinkageon ring,

When an upper terminal piece 30 is required forthe` spark pluginsulator, las shown-in Figs. 5and\6, the' layers i of powdered glassand'powdered iron can be positioned' by either method describedhereinbeforeand-'iired witlr the terminal element 30V resting on thetopsurface asshown in Fig', 5. The weight of the terminal element isnot-sufcie'ntto cause it tol sink into the fused andy sintered powderedmaterials duringV tiring, so that the assembly` must be removed from thelfurnace while-at the fusingtemperature `ot the glass and placed in ananvil 32 and"v pressedtogether by arbor Y34, soy that the terminalVelementislforced into the seal` until the shoulder 36 of theterminalzelement-contacts the top ofthe insulator. This requires manualhandling of red hot. partsv which is` notv convenient or desirable on aproduction line and also the high temperatures cause excessive oxidationof themetal parts when contacted by the atmosphere.- VThe powderedironalso tends to 'oxidize but, when'sintered under these conditions,vitis still van effective means to provide electrical contact between 'theterminal'element 30 and the; pigtail, andthereby illustrates one aspectwhereby one feature of the invention can be carried into practice. Theexternal application of mechanical pressure, at high` temperaturesdoesnot lend this modilication to application in a-,mass productionline.The bottom end 30A of the terminal piece is knurledto provideoverhangingportions which forma mechanical interlock with the sintered ironandifused glass toholdrthe-terrninal piece 30 vpermanentlyv in theinsulator bore. The sinterediron and fused glass tend to how-upwardlyalong the terminal piece as shown. in Fig. 6.-

Substantially theV sameresult can beV reached, although,` Y

not as eiciently, when the powdered glass andpowderedf iron are looselypoured around the pigtail and tired without: the compacting step, andwhenthe fused condition of the glass is reached, the terminal elementagain pushed down by mechanical pressure at thev high temperature. eThe: powdered/iron again becomes sintered and is effective to makecontact between the terminal element` and the pigtail.

The preferred` modification of the invention where an` upper terminalpiece is necessary yis shown in Fig. 7. Here a terminal. 40 is providedwitha sharpened lower end 42-and-knurling44, and also having ashoulder46 formed by a ange 48 to cooperate withethe upperend of the r insulator10as before. 'Otheryi/ise,VV the sealing element4 may be the same asinthe modification shown in Fig.`

1. 'Ihe Vpowdered borosilicate glass 24V and the *player 2.6 p

` The terminal piece 40 is thengprovided with asecondglass' element 50which cooperates with the bore 12. of theinu sulator above the ironpowder layer 26 and adjacent the `f knurled portion 44 to form amechanical interlock between the insulator bore and the terminal 40 topermanently hold it in position in the bore with the flange 48 restingon the insulator top. The glass element 50 is also in powdered formbefore firing and may be of the same glass type as the element 24 whichforms the seal about the pigtail or it may be of a different glasspreferably having a lower fusing temperature.

The glass, in powdered condition may be formed as a slurry with theaddition of water with or without a binding or oating agent andpositioned on the terminal element 40 by dipping to form a coatingthereon and then positioned in the bore of the insulator, so that theshoulder 46 rests on the insulator top while the pointed lower end 42pierces and is in close contact with the powdered iron layer 26. Thewhole assembly is then tired as before and will fuse together to formthe completed insulator without the use of mechanical pressure appliedat the high temperatures as disclosed with reference to the modicationshown in Figs. 5 and 6. The furnace will again have the reducingatmosphere to prevent yoxidation of the metal elements and can be madeto operate continuously with this modification. The upper glass element50 does not influence the seal, but provides a mechanical interlock forthe terminal piece to hold it permanently in position in the insulator.

Instead of forming a slurry of the powdered glass of the element 50, thepowdered glass can be poured in loose, dry condition in the bore 12 ofthe insulator 10 above the compacted iron powder 26, and the terminalelement 30 positioned therein by a turning motion until the shoulder 46rests on the insulator top and the tip 42 is in contact with the ironpowder layer. The assembly is then tired as before.

It is to be understood that the above detailed description of thepresent invention is intended to disclose an embodiment thereof to thoseskilled in the art, but that the invention is not to be construed aslimited in its application to the details of construction andarrangement of parts illustrated in the accompanying drawings, since theinvention is capable yof being practiced and carried out in various Wayswithout departing from the spirit of the invention. The language used inthe specification relating to the operation and function of the elementsof the invention is employed for purposes of description and not oflimitation, and it is not intended to limit the scope of the followingclaims beyond the requirements of the prior art.

What is claimed:

l. In a spark plug, a ceramic insulator consisting of a high percentage-of aluminum oxide having a central bore with a shoulder in anintermediate position, a lower electrode element having a head restingon said shoulder and extending downwardly to protrude from the lower endof the insulator to form a tiring tip, a metal pigtail permanentlyattached to the head of the electrode element and extending upwardly inthe bore of the insulator, a compacted element of powdered borosilicateglass positioned about the pigtail and in the adjacent portion of theinsulator bore to form a hermetic seal when fused in the bore, theexpansion coeicients of the metal of the pigtail, the glass of thesealing element, and the insulator being selected so that the fusedglass sealing element is under compression in the insulator bore in thenormal operating ranges of the spark plug, a layer of powdered metalcompacted in position above the powdered glass surrounding the upperterminus of the pigtail and making electrical contact therewith, aterminal element inserted in the upper end of the bore of the insulatorhaving a shoulder resting on the upper end of the insulator and havingan undercut portion extending downwardly to contact the powdered metalelement to establish electrical conductivity between the terminalelement and the lower tiring tip electrode element and having a layer ofagglomerated powdered glass adhering to at least a part of the terminalelement beneath the shoulder, said assembly being adapted to be heatedas a single step to fuse the powdered glass positioned adjacent themetal pigtail to form a hermetic seal for the bore of the insulator, andto sinter the powdered metal in the bore of the insulator to form acontactual means between the terminal and electrode element by engagingthe.` pigtail, and also to fuse the layer of powdered glass adhering tothe terminal element to mechanically interlock with the undercut portionto hold the terminal element in the bore of the insulator.

2. In a spark plug, a ceramic insulator consisting of a high percentageof aluminum oxide having a central bore with a shoulder in anintermediate position, a lower electrode element having a head restingon said shoulder and extending downwardly to protrude from the lower endof the insulator to form a tiring tip, a metal pigtail permanentlyattached to the head of the electrode element and extending upwardly inthe bore of the insulator, a powdered glass sealing element compacted inposition about the pigtail and in the adjacent portion of the insulatorbore to form a hermetic seal when fused in the bore, the expansioncoefficients of the metal of the pigtail, the glass of the sealingelement, and the insulator being selected so that the fused glasssealing element is under compression in the insulator bore in the normaloperating ranges of the spark plug, a layer of powdered metal compactedin position above the powdered glass surrounding the upper terminus ofthe pigtail and making electrical contact therewith, a terminal elementinserted in the upper end of the bore of the insulator having a shoulderresting on the upper end of the insulator and having a serrated portionextending downwardly to contact the powdered metal element to establishelectrical conductivity between the terminal element and the lowertiring tip electrode element and having a layer of powdered glassadhering to at least a part of the serrated portion of the terminalelement, said assembly being adapted to be heated as a single steptofuse the powdered glass positioned adjacent the metal pigtail to forma hermetic seal for the bore of the insulator, and to sinter thepowdered metal in the bore of the insulator to form a contactual meansbetween the terminal and electrode elements by engaging the pigtail, andalso to fuse the layer of powdered glass adhering to the terminalelement to mechanically interlock the terminal element in the bore ofthe insulator.

References Cited in the file of this patent UNITED STATES PATENTS2,100,187 Handrek Nov. 23, 1937 2,265,352 Corbin et al Dec. 23, 19412,267,571 McDougal Dec. 23, 1941 2,293,381 Carington Aug. 18, 19422,317,305 Schwartzwalder et al. Apr. 20, 1943 2,321,840 McDougal June15, 1943 2,436,644 Halstead Feb. 24, 1948 2,508,354 Brinson May 23, 19502,696,652 Cronin Dec. 14, 1954

